1. Field of the Invention
This invention lies in the technology of the manufacture of microstructures, which include such devices as microelectromechanical structures, micro opto-electromechanical structures, and semiconductor devices. In particular, this invention addresses gas-phase etching and deposition procedures, with particular emphasis on those involving the etching of silicon. This invention further addresses apparatus that is especially useful in meeting the needs of gas-phase etching and deposition.
2. Description of the Prior Art
The use of selective etchants to remove sacrificial layers or regions in a multilayer structure without removal of an adjacent layer or region is a necessary and common step in the manufacture of semiconductor devices, microelectromechanical structures (MEMS), and micro opto-electromechanical structures (MOEMS). MEMS and MOEMS have found applications in inertial measurement, pressure sensing, thermal measurement, micro-fluidics, optics, and radio-frequency communications, and the range of possibilities for these structures continues to grow. One example of such a structure is a reflective spatial light modulator, which is a device consisting of a planar array of electrostatically deflectable mirrors, each microscopic in size. The device is used as a microdisplay system for high-resolution, large-screen projection. In such a device, the sacrificial layer temporarily supports the mirror structure during the fabrication process. Once the mirror structure is formed, the sacrificial layer is removed to leave gaps below the mirrors and a microhinge along one edge of each mirror to join the mirror to the remainder of the structure. The gap and the microhinge provide the mirror with the freedom of movement needed for its deflection. Devices of this type are described in U.S. Pat. No. 5,835,256 (issued Nov. 10, 1998, to Andrew Huibers, assignor to Reflectivity, Inc., Santa Clara, Calif.). The contents of U.S. Pat. No. 5,835,256 are incorporated herein by reference.
The success of an etch step in the manufacture of microstructures depends on a number of factors, prominent among which are the completeness and uniformity of the etch among the areas to be etched, both across and throughout the microstructure surface. For deflectable mirror structures, the integrity of the microhinges (the structure undergoing mechanical deformation) is important to achieving uniform microstructure properties and a high yield of defect-free product. For other MEMS and for semiconductor devices, completeness and uniformity of the etch are likewise critical to insure that features on all areas of the structure function fully and property when in use. These factors are important in both isotropic and anisotropic etching. Isotropic etching is of particular interest, in structures where the purpose of the etch is to remove a sacrificial layer that is intervening between functional layers or between a functional layer and a substrate. The bulk of the sacrificial layer in these structures is accessible to the etchant only through vias in the functional layer and etchant must proceed laterally outward from the vias. The structures described in U.S. Pat. No. 5,835,256 above preferably employ isotropic etchant for this reason. The “vias” in these structures are the narrow gaps between the facing edges of adjacent mirror elements or between a mirror edge and an adjacent feature. Likewise, in the manufacture of any MEMS or semiconductor, all features on the structure surface must be fully defined and all materials that are not functional in the finished product must be fully removed.
Of potential relevance to certain embodiments of this invention is the prior art relating to particular etchant gases. Prominent among the etchants that are used for the removal of sacrificial layers or regions in both isotropic and anisotropic etching procedures are noble gas fluorides and halogen fluorides. These materials, used in the gas phase, selectively etch silicon relative to other materials such as silicon-containing compounds, non-silicon elements, and compounds of non-silicon elements. Descriptions of how these materials are used in etching procedures appear in co-pending U.S. patent application Ser. No. 09/427,841 and in portions of the present specification that follow. The invention claimed in application Ser. No. 09/427,841 offers an improvement in the selectivity of the silicon etch. Further means of improving the etch process particularly the uniformity and thoroughness of the etch, continue to be sought, since improvements in these features of the process significantly benefit the cost and reliability of the products manufactured.
The method of the present invention is useful for producing deflectable elements (deflectable by electrostatic or other means) which, if coated (before or after gas phase processing) with a reflective layer, can act as an actuatable micromirror. Arrays of such micromirrors can be provided for direct view or projection display systems (e.g. projection television or computer monitors). Also, if the micromirrors are provided alone or in an array and of a size of 100 micrometers or more (preferably 500 micrometers or more), the mirror is useful for steering light beams, such as in an optical switch. The present invention is also adaptable to processing (e.g. etching) semiconductor devices, and is not limited to MEMS devices.